The present disclosure relates to fuel injectors in a gas turbine engine and, more particularly, to the retention of components in a fuel injector nozzle.
A variety of devices and methods are known in the art for injecting fuel into gas turbine engines, many of which are directed to injecting fuel into combustors of gas turbine engines under high temperature conditions. Fuel injectors for gas turbine engines on an aircraft direct fuel from a manifold to a combustion chamber of a combustor. The fuel injector typically has an inlet fitting connected to the manifold for receiving the fuel, a fuel nozzle located within the combustor for spraying fuel into the combustion chamber, and a stem extending between and fluidly connecting the inlet fitting and the fuel nozzle. Fuel injectors are usually heat-shielded because of high operating temperatures arising from high temperature gas turbine compressor discharge air flowing around the stem and nozzle. The heat shielding helps prevent the fuel passing through the injector from coking, which can occur when the wetted wall temperatures of the fuel passage exceed a particular temperature. Coke in the fuel passages of the fuel injector can undesirably build up to restrict fuel flow to the nozzle and reduce the lifespan of the fuel injector.
A number of devices have been used to insulate the fuel passages in the nozzle from the relatively high temperatures outside the fuel nozzle, including the use of multiple annular stagnant air gaps between external walls (those in thermal contact with the relatively high temperatures outside the nozzle) and internal walls (those in thermal contact with the relatively cool temperatures of the fuel). Problems arise in fastening these walls together, for the fastener needs to be able to accommodate differing thermal expansion between the walls while holding the nozzle components together to prevent coking between the walls and wear due to vibration. Welds, braze, and/or pins are used, but welds and braze allow for direct conduction of heat between the external and internal walls, while pins provide additional wear surfaces that lead to damaging due to vibration. Additionally, welds, braze, and pins prevent the testing of the internal walls and other components within the external walls until the entire nozzle is constructed and make replacement of only one or a select number of internal components difficult because access to those components can only be achieved through the breaking of the welds and/or removal of the pins.